<div id="map"></div>

<script>
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v11',
        zoom: 0.1
    });

    var images = {
        'popup': 'https://docs.mapbox.com/mapbox-gl-js/assets/popup.png',
        'popup-debug':
            'https://docs.mapbox.com/mapbox-gl-js/assets/popup_debug.png'
    };

    loadImages(images, function(loadedImages) {
        map.on('load', function() {
            map.addImage('popup-debug', loadedImages['popup-debug'], {
                // The two (blue) columns of pixels that can be stretched horizontally:
                //   - the pixels between x: 25 and x: 55 can be stretched
                //   - the pixels between x: 85 and x: 115 can be stretched.
                stretchX: [
                    [25, 55],
                    [85, 115]
                ],
                // The one (red) row of pixels that can be stretched vertically:
                //   - the pixels between y: 25 and y: 100 can be stretched
                stretchY: [[25, 100]],
                // This part of the image that can contain text ([x1, y1, x2, y2]):
                content: [25, 25, 115, 100],
                // This is a high-dpi image:
                pixelRatio: 2
            });
            map.addImage('popup', loadedImages['popup'], {
                stretchX: [
                    [25, 55],
                    [85, 115]
                ],
                stretchY: [[25, 100]],
                content: [25, 25, 115, 100],
                pixelRatio: 2
            });

            map.addSource('points', {
                'type': 'geojson',
                'data': {
                    'type': 'FeatureCollection',
                    'features': [
                        {
                            'type': 'Feature',
                            'geometry': {
                                'type': 'Point',
                                'coordinates': [40, -30]
                            },
                            'properties': {
                                'image-name': 'popup-debug',
                                'name': 'Line 1\nLine 2\nLine 3'
                            }
                        },
                        {
                            'type': 'Feature',
                            'geometry': {
                                'type': 'Point',
                                'coordinates': [40, 30]
                            },
                            'properties': {
                                'image-name': 'popup',
                                'name': 'Line 1\nLine 2\nLine 3'
                            }
                        },
                        {
                            'type': 'Feature',
                            'geometry': {
                                'type': 'Point',
                                'coordinates': [-40, -30]
                            },
                            'properties': {
                                'image-name': 'popup-debug',
                                'name': 'One longer line'
                            }
                        },
                        {
                            'type': 'Feature',
                            'geometry': {
                                'type': 'Point',
                                'coordinates': [-40, 30]
                            },
                            'properties': {
                                'image-name': 'popup',
                                'name': 'One longer line'
                            }
                        }
                    ]
                }
            });
            map.addLayer({
                'id': 'points',
                'type': 'symbol',
                'source': 'points',
                'layout': {
                    'text-field': ['get', 'name'],
                    'icon-text-fit': 'both',
                    'icon-image': ['get', 'image-name'],
                    'icon-allow-overlap': true,
                    'text-allow-overlap': true
                }
            });

            // the original, unstretched image for comparison
            map.addSource('original', {
                'type': 'geojson',
                'data': {
                    'type': 'FeatureCollection',
                    'features': [
                        {
                            'type': 'Feature',
                            'geometry': {
                                'type': 'Point',
                                'coordinates': [0, -70]
                            }
                        }
                    ]
                }
            });
            map.addLayer({
                'id': 'original',
                'type': 'symbol',
                'source': 'original',
                'layout': {
                    'text-field': 'unstretched image',
                    'icon-image': 'popup-debug',
                    'icon-allow-overlap': true,
                    'text-allow-overlap': true
                }
            });
        });
    });

    function loadImages(urls, callback) {
        var results = {};
        for (var name in urls) {
            map.loadImage(urls[name], makeCallback(name));
        }

        function makeCallback(name) {
            return function(err, image) {
                results[name] = err ? null : image;

                // if all images are loaded, call the callback
                if (Object.keys(results).length === Object.keys(urls).length) {
                    callback(results);
                }
            };
        }
    }
</script>
